The Knowledge - Velocette Owners Club

# 5973 Originally it would have had a magnetic exhaust valve. However if you are going to the expense
of rebuilding the engine I would recommend new valves, even if it is just due to the fact that a ground
exhaust valve will sit even deeper in the no doubt pocked seat. Not such a performance issue on the
exhaust side, but certainly will be on the inlet.
# 5984 The original valve material is magnetic for both IN & EX. If you get new valves from the VOC the
EX will be higher spec than original. The material Veloce used was EN52 for both - and that is quite OK
for road use - the exhaust will suffer on unleaded fuel though but probably not enough to worry you. If
you intend to thrash it, get a better one. I would not sleeve cast iron valve guides though - get new.
Does your head man know what he's doing?
# 5930 I would be more concerned about the guy doing your head rather than the valve itself!
Providing the exhaust valve is not bi metallic, i.e. different materials for head and stem (check with a
magnet) it should be OK. It's probably 21/4N rather than Nimonic (although it could be a Venom valve
that is fitted as - while their head size is identical the length is not). Your inlet is probably EN52. If you
want to learn more visit the G & S Valves web site. Odds on your valve originated in their factory, as the
VOC, Grove, Dodkins, Uncle Tom Cobly and all source their valves from G & S.
http://www.gsvalves.co.uk/technical_information.htm The reason for the difference between the inlet
and exhaust valve and guide is that the stem diameters differ 3/8" for the exhaust 5/16" for the inlet,
plus there's also some minor detail differences in the guides. Everyone at some time should experience
the pure pleasure of replacing valve guides in iron heads. Just a big hammer and suitable drift -
guaranteed results each time with none of the stress of: Is the head the right temperature? Will it pick
up? Have I put it in too far / not far enough? By the way if your valve seats are pocketed in an iron
head, you can replace them with inserts. While the recess has to be machined accurately, its another
big hammer and drift job. Regards Dai Hello all, I have a question about valves for my 1937 MSS 500.
The guy who is redoing the valves on my cylider head said he is concerned because the exhast valve is
non magnetic. He says both valves are the same size... I notice my parts book says the intake is a
M2/4 and Exhaust is a M2/5 also I noticed the guides both have different part numbers... If they are the
same why the different numbers?
L # 6023 Hi guys. I thought that I would send a quick note to let you know how things are
progressing on my mkI KSS. Remember, the cam and skids wore out very quickly on it's first ride. I've
borrowed and bought some spares, and loosly assembled the bits on the workbench last night. When I
placed the cambox onto the head, I realized that the inlet tappet is not centered on the inlet valve. The
tappet is only hitting it halfway. I looked closer at the valve to see if it was bent, but it seems straight. It
appears that the tappet must have been putting a sideload onto the valve. That rocker broke at the
tappet, so the stresses must have been severe. The end of the valve has mushroomed quite a bit, and
now I cannot remove the valve from the guide without cutting the valve end off. So.... I'll try to fit my
cambox onto another head if possible, to see if they cambox or head is at fault. Does anybody have
any other ideas of what could have lead to this? Maybe the valve guide is in the head crooked, and
now the valve end is too far away from the tappets?
# 6025 The early Mk1s had a camshaft that had a much larger base circle diameter than later models,
the rocker skid inserts were correspondingly shorter than later models. If the cams and skids don't
match, the rocker will strike the valve at the wrong angle, and is possibly what your problem is. I am no
expert, and cannot tell you when the change occurred, or what the skid lengths or base diameters are,
perhaps someone else out there can oblige! I ended up adding oil jets aimed at the cams to cure the
rapid wear on my KTP, the head now is no longer in danger of going rusty!
# 6027 Has the inlet valve been pocketed into the head through too much seat grinding? It’s a common
problem with old K bits. If not is the valve the right length? A miss-match of bits eg followers, rockers,
cam will give problems with contact areas and angles on the rocker movement. Have you got the skids
& tappets sorted out? I now have some to measure if required.
L # 6182 I have just bought a 1967 Venom and have taken the head off to check there was no
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